In the textile industry, slivers or rovings are transported from and to drawframes, as well as fliers and spinning machines, in so-called spinning cans. After being filled or having run empty, each can must be replaced with a new empty or filled can as applicable. Optionally, the cans can be pulled or pushed singly or in groups on roller or sliding guides.
Modern spinning machines are supplied with the roving in so-called rectangular cans. These cans have standardized sizes and in principle a parallelepiped shape. They are positioned with their broad sides of the rectangles facing one another beneath the spinning stations or spindles of a spinning machine. In this so-called payout position, the roving, prepared to suit the applicable spinning process, is drawn out of a can at each spinning station. Once a can has run empty, it is replaced with a new full can. Since the cans are in self-contained rows side by side below the spinning stations, an empty can is first pulled out of the row and then replaced with a fill can.
For transporting the cans to and from the spinning stations, so-called can changing carriages are used. A can changing carriage retrieves and brings only as many full and empty cans each as it has a free space for at any time. This is necessary because on changing cans at the spinning machine, it must first take away an empty can (to create space for a full can) before it can place a full can in a payout position of the spinning machine.
The can changing carriage travels on a drive track, along the row of cans to be served, usually between two rows of spinning machines. It should not be substantially wider--measured crosswise to the drive track--than the can length; can length means the longest side of the rectangle, measured parallel to the can bottom, while can width is the length of the shortest side of the rectangle, measured parallel to the can bottom. The can changing carriage can have a width equal to the can length, if it is intended to hold and transport the cans in the same orientation (crosswise to the drive track) as that in which they stand in the can row in the payout position. However, the carriage should not be substantially wider than the can length, because otherwise the spacing from one spinning machine to another or one row of cans to another in adjacent rows of spinning machines would have to be correspondingly greater. Conventionally, can changing has been done manually, since the free space along the travel path of the can changing carriage has not seemed to afford enough space for mechanical apparatus and gripper, there not being sufficient space to insert grippers between the cans, which are packed flush with one another in a row.
In German Patent Disclosure DE 40 15 938 A1, a special short side can construction is made a prerequisite; on one long end, it has a lever with a sliver guide. The lever is secured to a short side of the can with the aid of a rod. Each can can be pulled out of its position below the spinning machine by being grasped by the rod. To that end, a can manipulator that contains a telescope is provided, which with the aid of a slide encompasses and by a single telescoping motion pulls it onto the vehicle away from the central plane of the spinning machine.
Accordingly, the prior art discloses a kind of trolley, which can be moved toward the applicable can with the aid of a telescope. A lifting device with a (single) horizontal gripper is secured to this trolley. For operation, four different drive mechanisms are necessary, namely drive mechanisms for the telescope, the trolley, a turning cylinder, and a lifting cylinder.
Another disadvantage of the arrangement described in the aforementioned reference DE 40 15 938 A1 is that with the manipulator, the applicable can can be unloaded only from the same side of the carriage as that which had received it in the first place. As a consequence of the known arrangement, the can is "lifted", since the single gripper seated on its trolley engages it from below. Hence the gripper cannot move past the can that has been placed on the carriage, and therefore it can remove the can only from the same side of the carriage by way of which it had loaded the can initially.
In German Patent Disclosure DE 43 33 775, a pivotable gripper is described that at the same time can advance two round cans, one empty and one full can, that are standing below the sliver depositor of a drawframe, by one can width fast enough that the sliver being paid out is not interrupted. This reference indeed has two grippers, but the two grippers are always in use simultaneously, so that in the final analysis, only one gripper for each can is available.